In telecommunications, modulation is the process of varying a periodic waveform (such as a local oscillator (LO) signal or a radio frequency (RF) signal represented as a high-frequency (HF) sinusoid waveform) to convey a message with the signal. A sine wave has three parameters—amplitude, frequency, and phase—which may all be modified according to a control signal, e.g., a low-frequency information signal, to obtain the modulated signal. An electronic device that performs modulation is generally known as a modulator. An electronic device that performs the inverse operation of modulation is generally known as a demodulator.
There are various techniques for the modulation process, one of which is digital modulation. With digital modulation, an analog carrier signal is modulated by a digital bit stream. Example digital modulation techniques include amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK).